Chemical pump

use

        It is widely used in industrial and urban water supply and drainage, and can also be used for irrigation and drainage of farmland and orchard for the transportation of clean water or other liquids with physical and chemical properties similar to clean water.

        classification

        According to the different chemical pump materials, the application fields are classified as follows:

        1) Chemical pumps (stainless steel) are widely used in petroleum, chemical, metallurgy, synthetic fiber, pharmaceutical, food, synthetic fiber and other sectors for the transport of alkaline corrosive media;

        2) Chemical pump (fluorine plastic material) is used to transport any acidic and alkaline corrosive medium;

        3) Chemical pump (cast iron material) is used for industrial, urban water supply and drainage, and can also be used for irrigation and drainage of farmland and orchard for transporting clean water or other liquids with physical and chemical properties similar to clean water.

        According to the different uses of chemical pumps, the classification is detailed:

        1) Process flow pump: including feed pump, return pump, circulation pump, flushing pump, sewage pump, supplementary pump, output pump, etc.

        2) Utility pump: including boiler pump, cold water tower pump, fire pump, deep well pump for water source, etc.

        3) Auxiliary pump: including lubricating oil pump, sealing oil pump, hydraulic transmission pump, etc.

        4) Pipeline pump: pump for oil pipeline, pump for loading and unloading truck, etc.

        Classified according to working principle and structure:

        1) Vane pump: When the pump shaft rotates, it drives various impeller blades to give liquid to the pipeline or container by centrifugal force or axial force, such as centrifugal pump, vortex pump, mixed flow pump and axial flow pump.

        2) Positive displacement pump: A pump that uses a continuous change in the volume of the pump cylinder to deliver liquid, such as a reciprocating pump, a piston pump, a gear pump, and a screw pump.

        3) Other types of pumps: electromagnetic pumps that use electromagnetic energy to transport liquid electrical conductors; pumps that use fluid energy to transport liquids, such as jet pumps, air lifters, and the like.

        Classified by transport medium:

        1) Water pump: including clean water pump, boiler feed water pump, condensate pump and hot water pump.

        2) Corrosion-resistant pumps: including stainless steel pumps, high-silicon cast iron pumps, ceramic acid-resistant pumps, impervious graphite pumps, lined hard rubber pumps, hard PVC pumps, shielded pumps, diaphragm pumps, titanium pumps, etc.

        3) Impurity pump: including slurry pump, sand pump, sewage pump, pulverized coal pump, ash pump, etc.

        4) Oil pump: cold oil pump, hot oil pump, submersible oil pump, oil slurry pump, liquid hydrocarbon pump, etc.

        Classified by usage conditions:

        1) Large flow and micro flow pump: flow rate is 300m & sup3; / min and 0.O1L / min;

        2) High temperature pump and cryopump: high temperature up to 500 ° C, low temperature to one Z53 ° C;

        3) High pressure pump and low pressure pump: high pressure up to 200MPa, vacuum degree is 2.66--10.66kPa (20-80mmHg);

        4) High-speed pump and low-speed pump: high speed up to 24000r / min, low speed 5-10r / min;

        5 3%; Accurate metering pump: flow metering accuracy of ± 0.3%;

        6) High viscosity pump: viscosity up to several thousand pascals (Pa•s).

        working principle

        Negative pressure pump

        The suction tube and pump must be filled with liquid before the pump is turned on. After the pump is turned on, the impeller rotates at a high speed, and the liquid rotates with the blade. Under the action of the centrifugal force, it flies outward from the impeller, and the liquid that is ejected in the pump chamber diffuses slowly, the pressure gradually increases, and then the pump At the exit, the discharge pipe flows out. At this time, at the center of the blade, the liquid is drawn to the surroundings to form a vacuum low-pressure zone with neither air nor liquid. The liquid in the liquid pool flows into the pump through the suction pipe under the action of the atmospheric pressure of the pool surface, and the liquid is continuous. It is continuously sucked from the liquid pool and continuously flows out from the discharge pipe.

        Positive pressure pump

        Mainly refers to the working principle of the submerged pump. The submersible pump and the long shaft submerged pump are used as an example. The submersible pump immerses the motor and the pump together in the bottom of the tank. The motor drives the impeller to push the medium to the ground target, and the long shaft liquid The pump connects the pump and the motor separately with a long shaft. The working principle is that the medium is transported under positive pressure, thus solving the problem of air resistance generated by the negative pressure conveying medium and the cavitation problem of the impeller. The motor of the submersible pump is not on the liquid surface, but under the liquid surface. The motor is a submersible motor and is connected to the pump wheel into a potential liquid. The main advantage of this design is that the bearing of the pump is only a few hundred millimeters, there is no long axis, there is no swing problem, the operation is stable, the sound is very small, almost no abrasion.

        The chemical pump seal forms mainly include: oil seal seal, gasket seal, thread seal, labyrinth seal, packing seal and dynamic seal, mechanical seal.

        Oil seal

        The utility model relates to a self-tightening lip seal, which has the advantages of simple structure, small size, low cost, convenient maintenance and small resistance torque, which can prevent medium leakage, prevent external dust and other harmful substances from invading, and has wear resistance. A certain compensation capacity, but not high pressure, so it is generally used in chemical pumps on low pressure occasions.

        Gasket seal

        The gasket is the basic component of the centrifugal pump static seal and is used in a wide range of applications. The selection of gaskets is mainly determined by factors such as the transport medium, temperature, pressure and corrosivity of the chemical pump.

        Thread seal

        There are generally two forms on chemical pumps, one is a threaded joint gasket seal, and the other is a threaded and filled seal, both of which are used for sealing of small diameter threaded joints. The seal of the threaded electric diaphragm pump gasket is a gasket, and the thread only serves to provide a pressing force.

        Labyrinth seal

        The maze sealing effect is very good when the design is reasonable, the processing is excellent, the assembly is good, and the rotation speed is high. However, in practical applications, the resulting chemical pump leaks are numerous, so it is not commonly used in chemical pump seals.

        Packing seal

        The filler with compressibility and resilience is placed in the stuffing box, and the axial pressing force of the gland is converted into a radial sealing force, thereby sealing.

        This method of sealing is called a packing seal and this packing is called a packing. Because the packing sealing structure is simple in form, convenient to replace, low in price, suitable for speed, pressure and wide medium, it is widely used in the design of chemical pumps.

        Dynamic seal

        When the chemical pump is in operation, the indenter generated by the auxiliary impeller balances the high pressure liquid at the outlet of the main impeller to achieve sealing. When parking, the auxiliary impeller does not work, so it must be equipped with a parking seal to solve the chemical pump leakage that may occur when parking.

        The auxiliary impeller has a simple sealing structure, reliable sealing and long service life. The drip water can be prevented from leaking during the operation of the chemical pump, so it is often used in the pump of the chemical pump to transport the impurity-containing medium.

        Machinery Seal

        Nowadays, the chemical pump industry is the most widely used sealing form. Because mechanical seals have the advantages of less leakage and long life, mechanical seals in the world are the most important shaft sealing methods in these equipments. Mechanical seals, also known as end seals, are defined in the relevant national standards: “The at least one pair of end faces perpendicular to the axis of rotation are held together by the action of the fluid pressure and the compensating mechanism's spring force (or magnetic force) and the auxiliary seal. a device that prevents fluid leakage by sliding relative to each other."

        Technical parameter editing

        Corrosion has always been one of the most headaches of chemical equipment. If it is slightly careless, it will damage the equipment and cause accidents and even disasters. According to relevant statistics, about 60% of the destruction of chemical equipment is caused by corrosion. Therefore, in the selection of chemical pumps, we must first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a “universal material” and it is dangerous to hold a stainless steel pump regardless of the medium and environmental conditions. Here are some key points for material selection for some common chemical media:

        1. Sulfuric acid is one of the strong corrosive media, and sulfuric acid is an important industrial raw material with a wide range of uses. Different concentrations and temperatures of sulfuric acid have a great difference in corrosion of materials. For concentrated sulfuric acid with a concentration above 80% and temperature less than 80 °C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. Not suitable for pump valve materials; ordinary stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti) also has limited use of sulfuric acid media. Therefore, the pump valve for conveying sulfuric acid is usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (20 alloy). Fluoroplastics have good sulfuric acid resistance, and the use of a fluorine-lined pump (F46) is a more economical option.

        2. Hydrochloric acid Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high silicon iron can also be used only for 50 ° C, 30% hydrochloric acid. Contrary to metal materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choice for transporting hydrochloric acid.

        3. Nitric acid is generally destroyed by rapid corrosion in nitric acid. Stainless steel is the most widely used nitric acid resistant material. It has good corrosion resistance to all concentrations of nitric acid at normal temperature. It is worth mentioning that it contains molybdenum-containing stainless steel (such as 316). 316L) The corrosion resistance to nitric acid is not only not superior to ordinary stainless steel (such as 304, 321), and sometimes even worse. For high temperature nitric acid, titanium and titanium alloy materials are usually used.

        4. Acetic acid It is one of the most corrosive substances in organic acids. Ordinary steel will be severely corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. Molybdenum-containing 316 stainless steel can also be used for high temperature and thin Acetic acid vapor. High-alloy stainless steel pumps or fluoroplastic pumps are available for demanding requirements such as high temperature, high concentration acetic acid or other corrosive media.

        5. Alkali (Sodium Hydroxide) Steel is widely used in sodium hydroxide solutions below 80 ° C and 30% concentration. Many factories still use ordinary steel at 100 ° C and below 75%. Although the corrosion is increased, the economy is good. The corrosion resistance of ordinary stainless steel to lye has no obvious advantages compared with cast iron. Stainless steel is not recommended as long as a small amount of iron is allowed in the medium. For high-temperature alkaline liquids, titanium and titanium alloys or high-alloy stainless steels are often used.

        6. Ammonia (Ammonia Hydroxide) Most metals and non-metals are slightly corrosive in liquid ammonia and ammonia (ammonium hydroxide). Only copper and copper alloys should not be used.

        7. Brine (seawater) Ordinary steel has a low corrosion rate in sodium chloride solution and seawater and salt water, and generally needs to be protected by paint; all kinds of stainless steel also have a low uniform corrosion rate, but may cause local corrosion due to chloride ions. It is usually better to use 316 stainless steel.

        8. Alcohols, ketones, esters, ethers, common alcohols are methanol, ethanol, ethylene glycol, propanol, etc., ketone media are acetone, methyl ethyl ketone, etc., ester media have various methyl esters, B Ester, etc., ether medium is methyl ether, ether, dibutyl ether, etc., they are basically non-corrosive, common materials can be applied, and specific selection should also make reasonable choice according to the properties of the medium and related requirements. It is also worth noting that ketones, esters, and ethers are soluble in a variety of rubbers and avoid errors when selecting sealing materials.

        Cooling problem

        The transportation of high-temperature medium puts higher requirements on the structure, materials and auxiliary system of the pump. Let's talk about the cooling requirements of different temperature changes and the company's applicable pump type:

        1. For media with a temperature lower than 120 °C, there is usually no special cooling system, and the medium itself is used for lubrication and cooling. Such as IHG, ISWH chemical pump, PHG shielded chemical pump (protection level of shielded motor should exceed class H when over 90 °C); while CZ common type and IH chemical pump can achieve upper temperature limit of 140 °C~160 due to suspension structure °C; IHF lining fluorine pump can be used up to 200 °C; only CQB ordinary magnetic pump can not exceed 100 °C. It is worth mentioning that the medium that is easy to crystallize or contains particles should be equipped with a sealing surface flushing line (designed with an interface).

        2. For mediums above 120 °C and below 300 °C, a cooling chamber shall be provided on the pump cover. The sealing chamber shall also be connected to the coolant (with double mechanical seal). When the coolant is not allowed to penetrate into the medium, The medium should be cooled and connected (can be realized by a simple heat exchanger). In addition, the CQB-G high temperature magnetic pump can be used for high temperature media up to 280 °C.

        3. For high temperature medium above 300 °C, not only the pump head part needs to be cooled, but also the suspension bearing chamber should be equipped with a cooling system. The pump structure is generally in the form of a central support. The mechanical seal is preferably a metal bellows type, but the price is high (price It is more than 10 times that of a normal machine seal).

        Sealing problem

        No leakage is the eternal pursuit of chemical equipment. It is this requirement that has led to the expansion of the application of magnetic pumps and shielded pumps. However, there is still a long way to go before there is no leakage, such as the life of the magnetic pump isolation sleeve and the shielded pump shield, the pitting problem of the material, the reliability of the static seal, and so on. Some basic information on sealing is briefly introduced as follows:

        1. Sealing form For static sealing, there are usually only two types of gaskets and sealing rings, and the sealing ring is most widely used in O-rings. For dynamic sealing, chemical pumps rarely use packing seals, mainly mechanical seals. Mechanical seals are available in single and double end, balanced and unbalanced types. Balanced type is suitable for high pressure medium sealing (usually refers to pressures greater than 1.0 MPa). Double end machine seals are mainly used for high temperature, easy crystallization and viscosity. , with particles and toxic volatile medium, double-end machine seal should be injected into the sealed cavity, the pressure is generally higher than the medium pressure of 0.07 ~ 0.1MPa.

        2. Sealing material The material of the chemical pump static sealing is generally made of fluororubber. In special cases, the PTFE material is used. The material arrangement of the mechanical seal static and dynamic ring is more important. It is not the hard alloy to the hard alloy, the price is high. On the other hand, it is not reasonable to have no difference in hardness between the two, so it is best to treat them differently according to the characteristics of the medium.

        (Note: The typical configuration of the American Petroleum Institute API 610 eighth edition for mechanical seals and piping systems is detailed in Appendix D)

        Viscosity problem

        Viscosity of the medium